This study is concerned with a mycoplasma (M. meleagridis) which is congenitally transmitted in turkeys. The organism parasitizes and multiplies to high numbers in many tissues of the developing embryo. However, except for the airsacculitis produced, the deleterious effects of such infections are not readily apparent. Since the organism utilizes arginine as a sole source of energy (and arginine is an essential amino acid for the host) it is possible that a potential nutritionally deficient state may develop in the host. In turn, such changes may be sufficient to predispose the host to a leg weakness commonly seen in young turkeys. Studies thus far indicate that arginine concentration in the yolk of infected embryos is significantly reduced at the time of hatching. An accentuated incidence of leg deformity was observed in such poults fed a diet marginal in arginine. Currently we are exploring in greater detail the events occurring during late embryonic and early posthatching life of the poult which might lead to leg deformities.